1. Field of the Invention
The present invention relates to a numerical control apparatus for a machine which is operable both in the metric system of measurement and in the English system of measurement.
2. Description of the Background Art
There are cases wherein a machine tool controlled by a numerical control apparatus is built in a country using the metric system and is sold in a country using the English system. It is desirable that the machine tool be operable in the metric system when workers of a manufacturer build, adjust and preliminarily operate it.
Moreover, as numerical data which represent parameters such as feed amount and feed rate of basic movements of machine elements are to be preliminarily set by the maker, such numerical data are more easily expressed in the metric system of measurement when input into a memory of the control apparatus. The workers can thus quickly build the machine tool in an easy and safe manner.
A user of the machine tool creates a numerical control program which may also include numerical data representing such parameters as feed amount and feed rate for performing specific machinery operations on a workpiece or which may rely on such data previously input by the manufacturer. In the country using the English system of measurement, the user creates such a numerical control program which expressing the numerical data in the English system.
Therefore, it is desirable that the numerical control apparatus be able to control the machine tool with the numerical data expressed in the metric system for the basic movements of the machine elements and with the numerical data expressed in the English system for specific machinery operations.
There is known a numerical control apparatus for controlling a machine tool which is switchable to operate either in the metric system or in the English system of measurement. However, if the conventional numerical control apparatus is set to operate in the English system, all numerical data must be expressed in the English system. Therefore, the numerical data expressed in the metric system representing parameteres such as feed amount and feed rate of the basic movements need to be converted into the English system. Such conversion is time and labor consuming, and could be a cause of errors in the numerical data.